The invention is concerned with a method and apparatus for calibration and quality assurance of nuclear medicine imaging as e.g. radionuclide renography by means of a phantom. The invention is also concerned with an arrangement comprising the apparatus of the invention.
The quality of nuclear medicine imaging, as in all imaging modalities, depends on the whole investigation procedure. If any of the steps is unsatisfactory, the result is not reliable. Most of the individual steps and the facility can, and should, be checked by employees of departments regularly, but this is not enough. The need for overall quality assurance by independent outside observers is taking place in medical imaging.
The basic principle of diagnostic nuclear medicine is the use of pharmaceuticals capable of carrying radionuclides that emit penetrating radiation. First the radionuclide and the pharmaceutical are combined, then the compound is injected into the circulatory system of the patient. The distribution of the radiopharmaceutical within the body can then be detected using a gamma camera to image and quantify regional physiological biochemical processes. For example dynamic radionuclide renal imaging (renography) gives functional and structural information about the kidneys and the urinary tract non-invasively.
The best way to compare the quality of imaging between laboratories is a multicentre study with a human being afflicted with known diseases. Due to ethical aspects and radiation safety it is, however, not possible. An analogue approach is to use organ-like phantoms. Zubovskii et al. (Zubovskii G A. Devishev M I, Ivanov E V, Andreeva O V and Luchkov A B 1983 Radionuclide studies with a dynamic kidney phantom Med. Radiol. (Mosk) 28 77-82 (in Russian)) have developed a renography phantom based on the flow itself of the radioactive liquid. No quantitative comparison with patient studies or repeatability of the phantom simulations exist. Neither is there presented any solutions for controlling of the flow of the radioactive solution inside the simulated organs to ensure repeatability.
Other kinds of dynamic phantoms exist. Sulab Oy in Helsinki, Finland is marketing a dynamic cardiac phantom (model DCP-101), wherein the cardiac function of the heart is simulated by moving lead shields. The degree of shielding of the radioactive ventricle area determines the ejection fraction. CAPINTEC, INC. sells a cardiac phantom (CP-201 Vanderbilt cardiac phantom), in which rotating ellipsoids simulate dynamic left atrium and verticle motion at variable heart rates. A variety of patient conditions can be simulated by varying the concentration of the radioactive solution in the ellipsoids and by adjusting the rate of rotation (variable pulse rate) and attenuator thickness. Static background represents the right heart chambers, aorta and general background tissues.
There are commercially available phantoms also for example for studying of brain perfusion single photon emission tomography (SPET) and bones but no commercially available renography phantoms for external quality assurance purposes.
An object of this invention is therefore the developing of a new phantom, with which it is possible to simulate different patient situations and organs.
Another object of this invention is the developing of a phantom, with which the flows and mixing of the radiopharmaceutical can be controlled and repeatability is possible.
To achieve the objects of the invention, there is has been developed a method for calibration and/or quality assurance of nuclear medicine imaging, in which functional information of the organs to be studied is achieved by inserting radioactive solution emitting detectable radiation in the organs of a phantom simulating the organs to be studied, and by detecting the radiation, which is mainly characterized in that the filling and emptying of the organs of the phantom to be studied is simulated by regulation of the detectable radiation from the phantom by successively removing respective adding isolating parts between the phantom and the detector of the radiation.
The arrangement of the invention mainly comprises a phantom simulating the organs to be studied and a gamma camera for detecting of the radiation and imaging of the organs. The organs to be simulated by the phantom are in form of containers filled with radioactive solution, and the phantom further comprises movable isolating parts between the containers and the gamma camera to isolate radiation from the containers to the camera.
In the preferred embodiments, the regulation of the detectable radiation is carried out in accordance with an exact time schedule to simulate a given patient situation. For example regional time activity curves over the kidneys and the heart can be used to calibrate analysis programs. The phantom can also be used in quality assurance between several laboratories by comparing clinical protocols, analysis programs and reports. The organs to be simulated by the phantom are the heart, the kidneys and/or the bladder. Additional organs to be simulated by the phantom can be the spleen, the liver, the ureters and soft tissues. The radiation is detected and imaged by a gamma camera during the simulation of the distribution of radio active solution to the body.
Before the method is started all radiation from the phantom is preferably isolated to simulate a situation before the entrance of the radio active solution to the body. The isolating is carried out by a lead plate between the phantom and the gamma camera. The method is then started by moving out the lead plate between the phantom and the gamma camera to expose the organ or organs to be studied. First, the upper body is studied and the rest of the lead plate is moved when the rest of the body is studied.
At the start of the above exposure, the radiation between the organ to be studied and the gamma camera is isolated by e.g. movable steel plates between the organ to be studied and the gamma camera. The filling/emptying of the organ to be studied is simulated by successively moving the steel plates from/to the space between the organ to be studied and the gamma camera so that the increasing of the radiation simulates the filling of the organ with radio active solution and the decreasing of the radiation simulates the emptying of the organ to be studied from radio active solution. The moving parts can be controlled by using a computerized step motor and the functions and the shapes of the kidenys can be automated.
In the method of the invention the following steps during detecting the radiation from the phantom is carried in the preferred embodiment, wherein the kidneys, the heart and the bladder is simulate:
The containers simulating the organs to be studied are filled with a radioactive solution,
the lead layer between the gamma camera and the background container is pulled out to simulate the entrance of the radioactive solution to the heart,
radiation from the container simulating the heart is controlled with a moving attenuator situated between the container and the gamma camera,
the rest of the lead layer is pulled out, which mimics the entrance of the radiopharmaceutical to the systemic circulation,
the steel plates are moved manually or automatically following an exact time schedule from the space between the kidneys and the background simulating the filling of the kidneys,
after moving out of the steel plates, they are moved back to the space, simulating washout of the kidneys,
after the beginning of the kidney washout, the cartridge with the tubes simulating the ureters is placed in the space between the background and the gamma camera, and finally the radiation from the container simulating the bladder is controlled with a moving attenuator to mimic filling of the bladder.
In the phantom described in this study the repeatability is good because the dynamics of the simulated kidneys depends only on mechanical movement of the steel plates. For the dame reasons the dynamics is easy to change to simulate all possible clinical situations.
The use of the phantom in tests showed its usefulness in multicentre comparisons and the phantom has a high interoperator reproducibility. The transportation of the phantom is easy in one large box and the reproduction of the phantom and the filling of the activities takes about 1-2 h. The whole phantom can be used completely by other users after a short training.
In advantageous embodiments, the moving parts can be controlled using computerized step motors. In an automated embodiment, the user only select the desired shapes and functions and presses the start buttom.
The phantom is also useful in the calibration procedure of analysis programs for dynamic radionuclide renography as well as in muiticentre comparison.
In the following, the invention is described by means of figures and some examples of preferred embodiments of the device and method of the invention. It has to be noted that the intention of the following detailed description is only for illustrative purposes and that the invention is not restricted to the details thereof. The scope of the invention is presented by the claims.